Reduced helicopter landing load?

Situation:
A helicopter is coming in to land on the reinforced concrete roof of a
building. The roof is much larger than the diameter of the helicopter
blades. At the last minute, the pilot questions whether the roof is
strong enough to carry the weight of the helicopter. He decides to
proceed with the landing, but then to keep the blades rotating and
generating lift to reduce the load on the roof, while the passengers
get off.

Question: Does this work? Won't the lift from the blades be
translated into a downblast of air, that will hit the roof and exert
the same load on the roof? In fact, if the air rebounds upward, this
technique might increase the loading on the roof.

Or have I once again totally misunderstood the situation?
.

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